There is not a way to make something clickable with CSS, but a lot of times what you can do is attach a background image to something that is already clickable such as site title that is already linked to the blog home page or change the dimensions of an already existing links to essentially overlap an image.
In your case, what you did was essentially take the clickable part and move it off left by 500 pixels with this CSS:
#main-nav h1,#main-nav .description {
margin-left:-500px;
}
I would recommend using text-indent instead of margin-left there because a margin will affect the spacing of the blog directly whereas text-indent will only affect the text placement.
Try the following to see if it gets the end result you're looking for:
Remove this:
#main-nav {
background:url('http://bunandbiscuit.files.wordpress.com/2012/05/girlwdog_145x218_logo.jpg') no-repeat scroll 0 0 transparent;
margin:0;
padding-top:9em;
overflow:hidden;
position:absolute;
}
#main-nav h1,#main-nav .description {
margin-left:-500px;
}
Add this:
#main-nav h1.masthead a,
#main-nav h1.masthead a:hover {
display: block;
background:url('http://bunandbiscuit.files.wordpress.com/2012/05/girlwdog_145x218_logo.jpg') no-repeat;
width: 145px;
height: 218px;
text-indent: -9999px;
}
#main-nav .description {
text-indent: -9999px;}
#main-nav .menu-wrap {
margin-top: -14px;
}
It will work to restore the Oulipo settings where the site title (which you replaced with an image) and the main navigation are fixed in place because it removes "position:absolute" from "#main-nav". See that?
You're doing great! I think you got really far just by looking at other forums!